1. Field of the Invention
The present invention relates to an ink jet recording apparatus that discharges ink or another liquid onto a recording medium and thereby perform recording, and more specifically, it relates to an ink jet recording apparatus configured to circulate ink between an ink supply source and a recording head.
2. Description of the Related Art
In some ink jet recording apparatuses, a main ink tank is mounted not on a carriage but on a main body of the ink jet recording apparatus, and ink is supplied from the main ink tank, for example, through a tube, to a recording head mounted on the carriage. This system will be referred to as off-carriage tank system for descriptive purposes.
The off-carriage tank system is advantageous in that a carriage does not require a large space for disposing a main ink tank, and a large amount of ink to be supplied to a recording head can be stored without putting a heavy load on the scanning of the carriage.
However, it is known that, since this system includes a tube, ink evaporates from the tube and thereby thickens, air enters the tube and generates bubbles, and this affects the discharge of ink. In the case of pigment ink, pigment precipitates, for example, due to prolonged disuse, and the density of ink is thereby varied. To solve these problems, a recovery operation is performed in which a recording head is covered with a cap, the recording head is depressurized through the cap, ink is thereby sucked out of nozzles of the recording head, and thickened ink, bubbles, or precipitated pigment is discharged from the recording head together with ink. However, in such a recovery operation, ink discharged together with the harmful substances is wasted. This is one of problems to be solved.
There is proposed an ink jet recording apparatus in which an ink tank and a recording head are connected by an ink supply tube from the ink tank to the recording head and an ink reflux tube from the recording head to the ink tank. In this configuration, ink discharged from the recording head together with thickened ink, bubbles, or precipitated pigment is returned to the ink tank by circulating ink. Therefore, the waste of ink is prevented.
The configuration of circulatory supply has room for improvement, for example, in the arrangement of the tubes connecting the recording head and the ink tank. Since the tubes are moved or displaced with the scanning of the carriage, a space in which the tubes are moved needs to be secured. This leads to an increase in the size of the recording apparatus. In addition, the load on the carriage increases due to the movement or displacement of the tubes, and therefore a structure is required that can withstand the increased load (for example, use of a large motor).
To solve these problems, Japanese Patent Laid-Open No. 61-213159 discloses a configuration in which a sub-tank is mounted on a carriage, a circulatory ink supply route is divided into two sections, and the sections are connected as needed to supply ink. In this configuration, bubbles and the like are recovered to an ink tank together with circulated ink, and ink is not discharged wastefully, and in addition, the use of tubes does not affect the driving of the carriage.
However, in the configuration in which a circulatory ink supply route is divided, the connection and disconnection of sections depends on the demand of the head for replenishment with ink, and frequently connecting and disconnecting the sections leads to a decrease in recording speed. To reduce the frequency of connecting and disconnecting operations, the size of the sub-tank needs to be increased. However, increasing the size of the sub-tank increases the load on the carriage and makes this configuration meaningless. In addition, the configuration in which a supply-side tube and a circulation-side tube are connected and disconnected at the same time can increase the size of the ink jet recording apparatus in view of the structure and operation load.